I answer that, A thing is said to be necessary for a certain end in two ways. First, when the end cannot be without it; as food is necessary for the preservation of human life. Secondly, when the end is attained better and more conveniently, as a horse is necessary for a journey. In the first way it was not necessary that God should become incarnate for the restoration of human nature. For God with His omnipotent power could have restored human nature in many other ways. But in the second way it was necessary that God should become incarnate for the restoration of human nature. Hence Augustine says (De Trin. xii, 10): "We shall also show that other ways were not wanting to God, to Whose power all things are equally subject; but that there was not a more fitting way of healing our misery."
Now this may be viewed with respect to our "furtherance in good." First, with regard to faith, which is made more certain by believing God Himself Who speaks; hence Augustine says (De Civ. Dei xi, 2): "In order that man might journey more trustfully toward the truth, the Truth itself, the Son of God, having assumed human nature, established and founded faith." Secondly, with regard to hope, which is thereby greatly strengthened; hence Augustine says (De Trin. xiii): "Nothing was so necessary for raising our hope as to show us how deeply God loved us. And what could afford us a stronger proof of this than that the Son of God should become a partner with us of human nature?" Thirdly, with regard to charity, which is greatly enkindled by this; hence Augustine says (De Catech. Rudib. iv): "What greater cause is there of the Lord's coming than to show God's love for us?" And he afterwards adds: "If we have been slow to love, at least let us hasten to love in return." Fourthly, with regard to well-doing, in which He set us an example; hence Augustine says in a sermon (xxii de Temp.): "Man who might be seen was not to be followed; but God was to be followed, Who could not be seen. And therefore God was made man, that He Who might be seen by man, and Whom man might follow, might be shown to man." Fifthly, with regard to the full participation of the Divinity, which is the true bliss of man and end of human life; and this is bestowed upon us by Christ's humanity; for Augustine says in a sermon (xiii de Temp.): "Go was made man, that man might be made God."
So also was this useful for our "withdrawal from evil." First, because man is taught by it not to prefer the devil to himself, nor to honor him who is the author of sin; hence Augustine says (De Trin. xiii, 17): "Since human nature is so united to God as to become one person, let not these proud spirits dare to prefer themselves to man, because they have no bodies." Secondly, because we are thereby taught how great is man's dignity, lest we should sully it with sin; hence Augustine says (De Vera Relig. xvi): "God has proved to us how high a place human nature holds amongst creatures, inasmuch as He appeared to men as a true man." And Pope Leo says in a sermon on the Nativity (xxi): "Learn, O Christian, thy worth; and being made a partner of the Divine nature, refuse to return by evil deeds to your former worthlessness." Thirdly, because, "in order to do away with man's presumption, the grace of God is commended in Jesus Christ, though no merits of ours went before," as Augustine says (De Trin. xiii, 17). Fourthly, because "man's pride, which is the greatest stumbling-block to our clinging to God, can be convinced and cured by humility so great," as Augustine says in the same place. Fifthly, in order to free man from the thraldom of sin, which, as Augustine says (De Trin. xiii, 13), "ought to be done in such a way that the devil should be overcome by the justice of the man Jesus Christ," and this was done by Christ satisfying for us. Now a mere man could not have satisfied for the whole human race, and God was not bound to satisfy; hence it behooved Jesus Christ to be both God and man. Hence Pope Leo says in the same sermon: "Weakness is assumed by strength, lowliness by majesty, mortality by eternity, in order that one and the same Mediator of God and men might die in one and rise in the other---for this was our fitting remedy. Unless He was God, He would not have brought a remedy; and unless He was man, He would not have set an example."
And there are very many other advantages which accrued, above man's apprehension.
Reply to Objection 1: This reason has to do with the first kind of necessity, without which we cannot attain to the end.
Reply to Objection 2: Satisfaction may be said to be sufficient in two ways---first, perfectly, inasmuch as it is condign, being adequate to make good the fault committed, and in this way the satisfaction of a mere man cannot be sufficient for sin, both because the whole of human nature has been corrupted by sin, whereas the goodness of any person or persons could not be made up adequately for the harm done to the whole of the nature; and also because a sin committed against God has a kind of infinity from the infinity of the Divine majesty, because the greater the person we offend, the more grievous the offense. Hence for condign satisfaction it was necessary that the act of the one satisfying should have an infinite efficiency, as being of God and man. Secondly, man's satisfaction may be termed sufficient, imperfectly---i.e. in the acceptation of him who is content with it, even though it is not condign, and in this way the satisfaction of a mere man is sufficient. And forasmuch as every imperfect presupposes some perfect thing, by which it is sustained, hence it is that satisfaction of every mere man has its efficiency from the satisfaction of Christ.
Reply to Objection 3: By taking flesh, God did not lessen His majesty; and in consequence did not lessen the reason for reverencing Him, which is increased by the increase of knowledge of Him. But, on the contrary, inasmuch as He wished to draw nigh to us by taking flesh, He greatly drew us to know Him.
Whether, if man had not sinned, God would have become incarnate?
Objection 1: It would seem that if man had not sinned, God would still have become incarnate. For the cause remaining, the effect also remains. But as Augustine says (De Trin. xiii, 17): "Many other things are to be considered in the Incarnation of Christ besides absolution from sin"; and these were discussed above (A[2]). Therefore if man had not sinned, God would have become incarnate.
Objection 2: Further, it belongs to the omnipotence of the Divine power to perfect His works, and to manifest Himself by some infinite effect. But no mere creature can be called an infinite effect, since it is finite of its very essence. Now, seemingly, in the work of the Incarnation alone is an infinite effect of the Divine power manifested in a special manner by which power things infinitely distant are united, inasmuch as it has been brought about that man is God. And in this work especially the universe would seem to be perfected, inasmuch as the last creature---viz. man---is united to the first principle---viz. God. Therefore, even if man had not sinned, God would have become incarnate.
Objection 3: Further, human nature has not been made more capable of grace by sin. But after sin it is capable of the grace of union, which is the greatest grace. Therefore, if man had not sinned, human nature would have been capable of this grace; nor would God have withheld from human nature any good it was capable of. Therefore, if man had not sinned, God would have become incarnate.
Objection 4: Further, God's predestination is eternal. But it is said of Christ ( Rom. 1:4 ): "Who was predestined the Son of God in power." Therefore, even before sin, it was necessary that the Son of God should become incarnate, in order to fulfil God's predestination.
Objection 5: Further, the mystery of the Incarnation was revealed to the first man, as is plain from Gn. 2:23. "This now is bone of my bones," etc. which the Apostle says is "a great sacrament . . . in Christ and in the Church," as is plain from Eph. 5:32. But man could not be fore-conscious of his fall, for the same reason that the angels could not, as Augustine proves (Gen. ad lit. xi, 18). Therefore, even if man had not sinned, God would have become incarnate.
On the contrary, Augustine says (De Verb. Apost. viii, 2), expounding what is set down in Lk. 19:10, "For the Son of Man is come to seek and to save that which was lost"; "Therefore, if man had not sinned, the Son of Man would not have come." And on 1 Tim. 1:15, "Christ Jesus came into this world to save sinners," a gloss says, "There was no cause of Christ's coming into the world, except to save sinners. Take away diseases, take away wounds, and there is no need of medicine."
I answer that, There are different opinions about this question. For some say that even if man had not sinned, the Son of Man would have become incarnate. Others assert the contrary, and seemingly our assent ought rather to be given to this opinion.
For such things as spring from God's will, and beyond the creature's due, can be made known to us only through being revealed in the Sacred Scripture, in which the Divine Will is made known to us. Hence, since everywhere in the Sacred Scripture the sin of the first man is assigned as the reason of the Incarnation, it is more in accordance with this to say that the work of the Incarnation was ordained by God as a remedy for sin; so that, had sin not existed, the Incarnation would not have been. And yet the power of God is not limited to this; even had sin not existed, God could have become incarnate.
Reply to Objection 1: All the other causes which are assigned in the preceding article have to do with a remedy for sin. For if man had not sinned, he would have been endowed with the light of Divine wisdom, and would have been perfected by God with the righteousness of justice in order to know and carry out everything needful. But because man, on deserting God, had stooped to corporeal things, it was necessary that God should take flesh, and by corporeal things should afford him the remedy of salvation. Hence, on Jn. 1:14, "And the Word was made flesh," St. Augustine says (Tract. ii): "Flesh had blinded thee, flesh heals thee; for Christ came and overthrew the vices of the flesh."
Reply to Objection 2: The infinity of Divine power is shown in the mode of production of things from nothing. Again, it suffices for the perfection of the universe that the creature be ordained in a natural manner to God as to an end. But that a creature should be united to God in person exceeds the limits of the perfection of nature.
Reply to Objection 3: A double capability may be remarked in human nature: one, in respect of the order of natural power, and this is always fulfilled by God, Who apportions to each according to its natural capability; the other in respect to the order of the Divine power, which all creatures implicitly obey; and the capability we speak of pertains to this. But God does not fulfil all such capabilities, otherwise God could do only what He has done in creatures, and this is false, as stated above (FP, Q[105], A[6]). But there is no reason why human nature should not have been raised to something greater after sin. For God allows evils to happen in order to bring a greater good therefrom; hence it is written ( Rom. 5:20 ): "Where sin abounded, grace did more abound." Hence, too, in the blessing of the Paschal candle, we say: "O happy fault, that merited such and so great a Redeemer!"
Reply to Objection 4: Predestination presupposes the foreknowledge of future things; and hence, as God predestines the salvation of anyone to be brought about by the prayers of others, so also He predestined the work of the Incarnation to be the remedy of human sin.
Reply to Objection 5: Nothing prevents an effect from being revealed to one to whom the cause is not revealed. Hence, the mystery of the Incarnation could be revealed to the first man without his being fore-conscious of his fall. For not everyone who knows the effect knows the cause.
Whether God became incarnate in order to take away actual sin, rather than to take away original sin?
Objection 1: It would seem that God became incarnate as a remedy for actual sins rather than for original sin. For the more grievous the sin, the more it runs counter to man's salvation, for which God became incarnate. But actual sin is more grievous than original sin; for the lightest punishment is due to original sin, as Augustine says (Contra Julian. v, 11). Therefore the Incarnation of Christ is chiefly directed to taking away actual sins.
Objection 2: Further, pain of sense is not due to original sin, but merely pain of loss, as has been shown (FS, Q[87], A[5]). But Christ came to suffer the pain of sense on the Cross in satisfaction for sins---and not the pain of loss, for He had no defect of either the beatific vision or fruition. Therefore He came in order to take away actual sin rather than original sin.
Objection 3: Further, as Chrysostom says (De Compunctione Cordis ii, 3): "This must be the mind of the faithful servant, to account the benefits of his Lord, which have been bestowed on all alike, as though they were bestowed on himself alone. For as if speaking of himself alone, Paul writes to the Galatians 2:20 : 'Christ . . . loved me and delivered Himself for me.'" But our individual sins are actual sins; for original sin is the common sin. Therefore we ought to have this conviction, so as to believe that He has come chiefly for actual sins.